In modern private branch exchanges or telephone installations or systems, such as call centers, usually a plurality of telephony or communication terminals are connected to a central exchange unit, via telecommunication connections which are set up between individual communication terminals or also between calls coming in from outside the internal telephone network and selected communication terminals. Within the framework of these telecommunication connections, voice data or user data are transmitted to the respective selected telephony terminal and/or from the latter to the central exchange unit and from the central exchange unit to the respective terminal. The data can be transmitted in the conventional manner or else using an Internet Protocol.
In relatively complex telephone installations or systems, such as in call centers or the like, or in telephone systems in enterprises or organizational units, where the called communication terminal is not necessarily selected because of the person or the respective user, but because of the latter's subject-matter qualification or competence, the communication terminals can be organized or combined in groups, whereby a group telephone number selectable by the calling party can be allocated to each group. For example, in a call center, a group of communication terminals can be provided for the “Sales” function, a calling party or customer selecting a central telephone number provided for Sales and then being put through by an allocated exchange unit of the communication network to a communication terminal allocated to this group, to which a Sales employee can be reached. All communication terminals allocated to the respective group report their current availability to the exchange unit by means of their corresponding availability information. The exchange unit will then use the corresponding availability information to select a communication terminal allocated to the selected group that has an availability information indicating that it is available.
Private branch exchanges, in particular for call centers or contact centers, can also be designed for data transmission via multimedia applications or also via an Internet Protocol. In such systems, Session Initiation Protocol (SIP) can be used to set-up a communication connection. In using SIP, prior to the set-up of a communication connection, the communication modalities are configured to be able to exchange data between the communication terminals involved, i.e. in particular the calling communication terminal and the intended target communication terminal. The calling communication terminal sends a start message to the desired target communication terminal in which a request of a connection set-up is transmitted. The start message can provide additional information as well. If the desired target communication terminal is available, in which case a communication connection shall be set up, the target communication terminal will transmit a corresponding confirmation message. The corresponding confirmation message can also transmit additional information. Based on the information contained in the start and confirmation messages exchanged, criteria for the communication connection to be properly set-up and status information on the present or future availability of the communication party or the like can be transmitted. The desired communication connection can then be set up.
When applying such a SIP technology in complex telephone systems, such as, call centers or contact centers, an individual SIP address is usually allocated to each communication terminal so that data can be exchanged to a particular communication terminal for initiating a communication connection. A communication terminal integrated in such a way in the communication network through SIP is also called “SIP end point.” Each SIP end point is registered as a possible address for SIP messages.
When designing relatively complex telephone systems, in particular for call centers or contact centers, the service orientation or the achievement of a high customer satisfaction among the calling parties is of particular importance. If it is not possible, upon a customer's call, to immediately establish a contact to a correspondingly competent service employee, the calling party's wishes should be taken into account as much as possible, in view of a possible callback, a possible new call or the possibility of an automated inquiry. If a calling customer encounters the situation where no employee at the call center or contact center from the called service area is available, most call centers or contact centers usually switch over to a stored tape announcement, an answering machine, or the current call has to be interrupted temporarily. This can be unsatisfactory for the calling customers, in particular if their only option is a new call at a later time.